Author(s)

Shimmon Naim, Evgeny Griv

Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Ilan Ramon Physics Center, Ben-Gurion University of the Negev, Beer-Sheva, Israel.

The cluster M67 (= NGC 2682) in Cancer is a rich stellar cluster, usually classified as an open cluster. Using our own observations with the 0.4 m telescope, we show that M67 is a tight group of about 1200 stars. The actual radius of the cluster is about 3.1 pc and the average mass of a star in the system is about . We also show that the ratio of the mean kinetic energy of the cluster to its mean gravitational potential energy , while the value predicted by the virial theorem is equal to . So the system is a gravitationally bound. This value of is considered as an evidence of quasi-stability of the cluster and allows us to use the Chandrasekhar-Spitzer relaxation time for M67 Myr as a characteristic dynamical relaxation time of the system. As the cluster is almost twice older its half-life time , it is argued that M67 was in the past (about 4 Gyr ago, close to its forma-tion) a relatively small ( stars) globular cluster, but got “open cluster” shape due to the dynamical evapora-tion of the majority of its stars.

Photometers; Techniques; Photometric; Open Clusters and Associations; M67; Galaxies; Star Clusters

S. Naim and E. Griv, "Examining the M67 Classification as an Open Cluster," International Journal of Astronomy and Astrophysics, Vol. 2 No. 3, 2012, pp. 167-173. doi: 10.4236/ijaa.2012.23020.